1. Technical Field
The present disclosure relates to radio communication apparatuses and interference signal detection methods.
2. Description of the Related Art
In recent years, the range of uses to which wireless sensor networks is put has been expanded to include smart meters, home energy management systems (HEMS), medical care, social infrastructures, and so forth and has attracted attention. For example, in Japan, the 920 MHz band is assigned as the industry-science-medical (ISM) band, and the user can perform wireless sensor networks by using this frequency band without the need for a license.
The 920 MHz band is present near the 800 MHz band and the 900 MHz band which are assigned as the radio waves for mobile telephones. In particular, the frequency band from 945 MHz to 960 MHz is assigned for LTE communication and a signal formed of a plurality of OFDM modulated subcarriers is transmitted therein. There is a high possibility that, depending on the combination of the frequencies of these subcarriers, odd-order intermodulation distortion such as third-order intermodulation distortion or fifth-order intermodulation distortion occurs near the 920 MHz band and becomes an interference signal.
As described above, in the radio communication, the intermodulation distortion of the radio wave used in other communications may act as an interference signal and cause significant degradation in reception performance.
In Japanese Unexamined Patent Application Publication No. 2009-111848, as a method for detecting and removing an interference signal, a method by which a desired signal is removed by a notch filter and then an interference signal is detected has been proposed. Moreover, in Japanese Unexamined Patent Application Publication No. 2013-26970, a circuit that detects an interference signal having signal strength which is higher than or equal to predetermined signal strength has been proposed.